A slot serving 20,000 impressions and producing four clicks is not a mystery, but it is usually not the cause people guess first. Work through these in order — the common ones are at the top.

1. It is not being seen

The most frequent cause by a wide margin. The slot serves, the impression counts, and nobody scrolls that far.

Check: viewability. If you have it, compare viewable impressions to total. Below 40% is your answer.

No viewability data? Load your own page on a phone and see whether you reach the slot without deliberately scrolling for it. Most traffic is mobile, and a sidebar slot on a mobile layout often ends up below the entire article.

Fix: move it. Below the header or after the first two or three paragraphs.

2. The creative is bad

Small advertisers frequently supply a banner that is their logo on a coloured background with no offer and no reason to click.

Check: look at it. Can you tell what is being sold and why you would want it, in one second, at actual size on a phone?

Fix: ask for a second version with a clear offer and a visible call to action. Frame it as helping them, because it is. Many will not have thought about it and are glad to be told.

3. It looks like an ad, in the way people ignore

Readers have learned to skip anything that occupies a standard banner shape in a standard banner position. This is banner blindness, and it is real.

Check: is the slot a 728×90 at the very top, styled to look like every other 728×90?

Fix: try a native format — text plus a small image, in your site's typography, clearly labelled as sponsored. On a lot of small sites this outperforms display by a wide margin, because it gets read rather than skipped.

4. Frequency is too high

If the same hundred regulars see the same banner forty times each, they stopped noticing it in week one. Your impression count looks healthy and your reach is tiny.

Check: unique visitors against impressions. Frequency above 8–10 is the problem.

Fix: cap frequency at 3–5 per person per day, and rotate two or three creatives from the same sponsor.

5. The advertiser is a poor fit

Sometimes the audience genuinely does not want the product, and everything else is fine.

Check: has any other advertiser performed well in this slot? If a house ad for your newsletter gets 0.8% and the sponsor gets 0.05%, the slot works and the match does not.

Fix: tell the sponsor honestly. It is a better conversation than letting them conclude your site does not work.

6. Something is broken

Least common, but worth ruling out once the others are clear.

Check: click the ad yourself. Does it go where it should? Does the click register in your reports within a minute?

Common culprits: a destination URL with a typo, a click tracker blocked by the reader's browser, or a transparent element sitting on top of the slot and swallowing clicks. That last one is easy to spot — inspect the slot in dev tools and see what is actually on top at those coordinates.

The order matters

Publishers tend to start at 6 and work backwards, because a technical fault feels like the kind of thing that would cause an unusual result. In practice it is almost always 1 or 2, and both are cheap to check.

Load the page on your phone and look at the banner. That single step resolves most of these.

What good looks like

For a relevant direct sponsorship in a well-placed slot: 0.3% to 1.0% CTR. Anything in that range is working.

Below 0.1%, one of the six above is true. Above 2%, check that the slot is not adjacent to something people are trying to click on — accidental clicks are worse than no clicks, because the sponsor pays for traffic that bounces immediately and works out why.